Re: Still lacking

Posted by Leigh L. Klotz Jr WA5ZNU on
URL: http://elecraft.85.s1.nabble.com/Still-lacking-tp6419804p6429972.html

K7TV wrote

The battery can provide very high output current for a short time, I
believe enough to power a 100 W transmitter briefly.

Yes, LiFePO4 has a high power density but not as high energy density as LiPoly or the typical Li-Ion (laptop) batteries.  It was chosen for the One Laptop per Child project, for example.

The chemistry has a very flat discharge curve, and sources high current or low current, and retains its efficiency.  For SLA, the capacity is rated at a discharge rate of 1/20 C, so a 7AH SLA battery will give you 1A for 7 hours, but any transmit at 20A would be well beyond its capacity.  A 20AH SLA would give you 1A for 20 hours, and could give you 20A briefly, but not for 1 hour.  

But an 8AH LiFePO4 will have no trouble giving you 20A for 20-25 minutes solid key down.  With SSB 40% modulation at 100W and transmitting 1 minute out of 4, that gives you 10% duty cycle, and because of the excellent properties of LiFePO4 you'd get a a couple of hours of operating time easily, especially with the low RX current draw of the KX3.  

Couple the LiFePO4 with a solar panel that can cover the receive current (about $50) and you extend your QRV to pretty much all day with an 8AH pack or a couple of 4AH packs.

Leigh/WA5ZNU